Issue34

C. Baron Saiz et alii, Frattura ed Integrità Strutturale, 34 (2015) 608-621; DOI: 10.3221/IGF-ESIS.34.67 609 the convection mechanism of disc brakes [10-12], so to limit very high temperatures of the system. Ventilated disc brakes accomplish this purpose and, due to their braking stability, controllability and ability to provide a wide-range brake torque [10], they have been more and more used. Unlike full disks, they are designed with internal vanes that allow to drive greater amount of airflow through the disc. To continuously improve their performances, many new solutions have been proposed over the years by companies that produce disc brakes. In this paper, different geometries of ventilated rotors have been studied to estimate their performances by means of thermo-mechanical coupled analyses. A full disc has been also analysed, in order to quantify the advantages of using air channels in hard braking conditions. The work has been developed as follows: in the first step, a reverse engineering procedure has been setup to create the parametric CAD models of the analysed disc brakes. In this phase, moreover, the geometries of the discs have been suitably modified to compare, in the most correct and consistent way, the results. In the second step, using the Ansys FEM code, brake-fading tests have been simulated through coupled thermal-structural analyses [13,14]. In the last step, the results of all the analysed brake discs have been studied and compared in terms of temperature, strain and stress distributions. W ORKING CONDITIONS im of this work is to evaluate the effectiveness, in terms of thermomechanical performances, of different internal configurations of ventilated brake rotors. To achieve this purpose, the analysed brake discs have been subjected to very hard conditions using the Brembo fading test [15-16]. This test consists of fourteen repeated braking, from an initial velocity, Vi, of 160 km/h (44.44 m/s) to stop, with a constant deceleration. Between two following braking, there is a recovery time during which the rotor is initially accelerated and, subsequently, maintained at constant velocity Vi. Fig. 1 shows the acceleration versus time graph during the fading test. Figure 1 : Acceleration versus time in fading test. The recovery time, ∆t r, is established intentionally brief in order to stress the cooling capacity of the brakes. In Tab. 1, the most important input data of the fading test are summarized. All the analysed rotors are made of grey cast iron, one of the most common material commercially used for this kind of components. Main physical, thermal and mechanical characteristics are presented in Tab. 2. To better simulate the real behaviour of the material, the specific heat capacity, the thermal conductivity and the elastic modulus have been considered variable with the temperature, as shown in Figs. 2-4. As regards the case studies, three ventilated discs and a full one, all by Brembo, have been used. Vented rotors differ from each other in vanes shape. In particular, the three ventilated discs have, respectively, straight, curved and pillar-shaped vanes. Three-dimensional fully parametric CAD models [17] of the discs have been created from 2D technical drawings by Brembo [15], following a typical reverse engineering approach [18]. Irrelevant details have been removed to simplify the FEM models, so reducing the analysis computational time. Main sections of the ventilated discs and a frontal view of the full rotor are shown in Fig.5. A

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